Generally, a standard wheel-box test may be used for characterizing turbine blades; however, such known tests only partially address desires and needs for turbine blade design. For instance, the output of such tests only provide for measuring the natural frequencies of the system, with poor information about wheel\blade modal forms and forcing excitation. Consequently, standard wheel-box tests allow for only output-output analysis (e.g., the determination of the quality factor).
Additionally, in such standard wheel-box tests, the excitation is typically reproduced by means of a gas spray, and thus cannot be performed at too low of an absolute pressure. Further, it may be noted that the excitation forces produced with a gas spray are limited by the vacuum pump flow rate capability. This limit does not allow for using high spray flow rates and consequently does not allow for high impulse forces on the blades.
Consonant with the foregoing, the present inventors are unaware of any works modeling or characterizing (e.g., quantifying) a gas spray excitation (which excitation is very difficult to model), providing for complex characterization. The difficulties in modeling or characterizing the gas spray excitation (e.g., quantifying) also limits standard wheel-box testing; for example, this inability prevents designing and/or optimizing the excitation to excite one or more specific modes (e.g., as may be desired by a customer).
While software (e.g., LMS, B&K, AGILIS, etc.) is available for performing post-processing of test-data signals acquired during wheel-box tests and providing for the characterization of the modal shapes, such post-processing software represents a specific methodology of characterizing modal shapes and has various limitations. For instance, such post-processing software do not allow for closing the loop through the analysis of the excitation.
In other words, techniques for measuring, analyzing, and/or characterizing rotating blades (e.g., dynamic characterization of turbine blades) are generally limited to output-output type techniques and, for example, use neither excitation modeling nor input-output methodologies.